Should We Do Away With 'Wind Chill Factor'?

As cold weather grips much of the country, we’re hearing a lot about the “wind chill factor.”

The measurement comes from Canadian Antarctic explorers Paul Siple and Charles Passel, who in 1945 worked out an equation to show how quickly water froze at different temperatures depending on the wind.

The numbers that come out of their equation were the precursor to our modern day “wind chill factor,” which is supposed to tell you how cold it feels outside.

But Slate columnist Daniel Engber wants to see wind chill factor done away with completely. He argues that the number is arbitrary, and that factors such as sunlight, surrounding buildings and a person’s height and weight affect how temperature feels.

Critics of his argument say wind chill is a useful metric because it warns people when there is higher risk of hypothermia.

Engber joins Here & Now’s Meghna Chakrabarti to make his case against windchill.

UNIDENTIFIED WOMAN: And when you factor in the wind chill, it felt like minus-40.

UNIDENTIFIED MAN #2: However, the wind chill will make it feel much colder.

UNIDENTIFIED MAN #3: We're more in the lower range, where that wind chill is between minus-30 and minus-50.

(LAUGHTER)

CHAKRABARTI: Honestly, just I feel frozen just hearing that. But wind chill is something a lot of Americans have been hearing about over the past several days. But what does it really mean? Daniel Engber is a columnist for Slate.com, and he's done some digging into the fascinating backstory about the wind chill factor, and he joins us via Skype. Welcome.

DANIEL ENGBER: Thank you.

CHAKRABARTI: So you take us back to 1945 in your article and two Antarctic explorers named Paul Siple and Charles Passel. Who are they, and what did they do?

ENGBER: Well, these were the - sort of the originators of wind chill. They left plastic bottles of water outside in the wind, in the Arctic, and decided to see how quickly the water froze as a function of how windy it was. And they found that of course if it's very windy, the water would freeze faster.

CHAKRABARTI: So they calculated an equation off of this. American weathermen, if I understand this correctly, they converted those numbers into statements similar to what we hear today, such as the wind chill factor is, say, five below zero. But even those initially had some pretty broad inconsistencies, didn't they?

ENGBER: There were some inconsistencies. People noticed that the forecasters might say it's going to feel like, you know, minus-50, and it really - just that didn't seem right. And so in 2001, the wind chill was sort of reformed or updated so the numbers would make more sense.

But the point that I make in this piece and that I make to anyone who'll listen is that even the system we have now is fairly ridiculous and doesn't really tell you anything useful about how you might feel on any given day.

CHAKRABARTI: Well, given the weather we've been having across a lot of the country in recent days, I think a lot of people will listen to you now.

(LAUGHTER)

ENGBER: Right.

CHAKRABARTI: So, I mean, what about it in particular do you object to? What makes it so sort of incomprehensible?

ENGBER: Well, it makes all of these assumptions. There are these assumptions that go into the calculation that I think most people don't know about. It assumes that you're walking around outside in the dead of night, ignoring the fact that, you know, there might be sunlight. Sunlight can make you feel maybe 10 to 15 degrees warmer.

It's assuming you're walking at three miles an hour directly into the wind. It's assuming there are no obstacles around you. If you're in Boston or New York City, you're probably surrounded by buildings. It's based on wind speed readings that are taken at the top of 30-foot poles and then adjusted for an estimation of what it might feel like hitting your face at five feet above the ground. So that suggests that it's assuming that you're five feet tall.

And finally it assumes that you're overweight, if not obese, which affects the rate at which heat might escape from the skin of your face. As you can see, there are all of these assumptions that go into it. And if it's so specific to those assumptions, then why are they even telling me how I'm going to feel when I'm not five feet tall, I'm not obese, I live in a city, and I'm walking around in the daytime?

CHAKRABARTI: I had no idea that those - all those assumptions were in wind chill, I mean, because it's - in weather conditions such as we're currently seeing, it's like an almost ubiquitously used phrase. And I mean, I'm getting the feeling, Daniel, that you would just prefer it if newscasters, weathermen and -women and meteorologists in general just stopped using wind chill.

ENGBER: Well yeah, I mean, I want to make one thing clear, which is when it's windy out, it does feel colder. I mean, that's so obvious it's not even worth saying. But the numbers that are put on it are just not useful. I think they should tell you it's going to be 12 degrees and very windy, and people would know that that means it's 12 degrees, and it's going to be really cold, just as you know if they say it's 12 degrees and sunny you know it's going to be quite as bad.

So, you know, there are all these other things that the weather reporter will tell you about sun and precipitation. Of course if it's a wet and windy day, that's going to be even worse. So you get all of these factors that will affect how you feel. They're presented as individual factors. And they don't try to combine all of those into a single number that's almost certainly going to be invalid for you.

CHAKRABARTI: But if I may, though, Daniel, I mean part of what I find to be somewhat useful about wind chill is that it does give you sort of this sense that we're seeing a dramatic weather event. And in part, I mean, when the wind is blowing, and it does feel colder than usual, I mean, maybe it's a good way to say hey, be careful when you go outside because, you know, hypothermia can set in before you know it, especially in these kinds of conditions.

ENGBER: Well, there's - I sort of have two responses to that. So the first is yes, there are real dangers, and some of those dangers are exacerbated by wind. And so to highlight the fact that it's not only cold but a windy cold, and so you'll get frostbite more quickly, that's important. I just don't think that this feels-like temperature is a useful way to go about doing that. You could just say, as the Weather Service sometimes does, that exposed skin will freeze in 20 minutes given the wind and temperature.

I mean that - those are numbers that are specific and useful and are given out. I mean, these are things that would be very useful, but there are these misleading situations. So if the temperature, say, were 35 degrees, but the wind chill were 15, you're in a situation where no matter how long you're outside, you're just not going to get frostbite because the temperature is above freezing.

So you can actually create a misleading sense of risk when you start reporting these gaudy wind chill numbers that doesn't really help anyone.

CHAKRABARTI: Well, Daniel Engber is a columnist for Slate.com, educating on the ins and outs of wind chill. Daniel, thank you so much.

ENGBER: Thanks for having me.

ROBIN YOUNG, HOST:

And Meghna, we're hearing from listeners. Roger Bacon(ph) writes: Weather should be described in absolutes, no more wind chill. But I'm wondering, don't some people feel this is a competition? I mean, aren't we all trying to prove we have the lowest temperatures? So we want to know your thoughts on wind chill at hereandnow.org. Transcript provided by NPR, Copyright NPR.